Using CLI Help

Using CLI Help
The IOS has several forms of help available:
Context-sensitive help
Command Syntax Check
Hot Keys and Shortcuts

Context-Sensitive Help
The context-sensitive help provides a list of commands and the arguments associated with those commands within the context of the current mode. To access context-sensitive help, enter a question mark, ?, at any prompt. There is an immediate response without the need to use the key.

One use of context-sensitive help is to get a list of available commands. This can be used when you are unsure of the name for a command or you want to see if the IOS supports a particular command in a particular mode.

For example, to list the commands available at the user EXEC level, type a question mark ? at the Router> prompt.

Another use of context-sensitive help is to display a list of commands or keywords that start with a specific character or characters. After entering a character sequence, if a question mark is immediately entered-without a space-the IOS will display a list of commands or keywords for this context that start with the characters that were entered.

For example, enter sh? to get a list of commands that begin with the character sequence sh.

A final type of context-sensitive help is used to determine which options, keywords, or arguments are matched with a specific command. When entering a command, enter a space followed by a ? to determine what can or should be entered next.

As shown in the figure, after entering the command clock set 19:50:00, we can enter the ? to determine the options or keywords that fit with this command.

Command Syntax Check
When a command is submitted by pressing the key, the command line interpreter parses the command from left to right to determine what action is being requested. The IOS generally only provides negative feedback. If the interpreter understands the command, the requested action is executed and the CLI returns to the appropriate prompt. However, if the interpreter cannot understand the command being entered, it will provide feedback describing what is wrong with the command.

There are three different types of error messages:
Ambiguous command
Incomplete command
Incorrect command

Using CLI Help

Using CLI Help
Using CLI Help 
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